Altering the exposed facet of CeO2 nanocrystallites and hence the control of surface chemistry on the nano level have been shown to significantly change their performances in various catalytic reactions. The chemical state of surface Ce, which is associated with Lewis acidity and hence the adsorption/activation energy of reactants on the surface, is expected to vary with their hosted facets. Unfortunately, traditional surface tools fail to differentiate/quantify them among hosted facets and thus have led to different interpretations among researchers in the past decades. Herein, probe-assisted nuclear magnetic resonance is employed for the surface investigation of different CeO2 facets. They not only allow differentiation of the surface Ce atoms between hosted facets at high resolution but can also provide their corresponding concentrations. The as-established facet fingerprint of CeO2 can thus report on the facet distribution/concentration of a given CeO2 sample. Dephosphorylation and H2O2 reduction were tested as probe reactions to demonstrate the importance of obtaining comprehensive surface Ce information for the active site identification and the rational design of CeO2-based catalysts. Around 1000 and 4500% increase in activity of those reactions can be easily achieved on pristine CeO2 without further surface engineering when its terminal facet is wisely chosen. Our results thus imply that the basic surface knowledge of even a simple catalyst can be more important than the continuous development of their fancy derivatives without clear guidance.
Transition metal doped chalcogenides are one of the most important classes of catalysts that have been attracting increasing attention for petrochemical and energy related chemical transformations due to their unique physiochemical properties. For practical applications, achieving maximum atom utilization by homogeneous dispersion of metals on the surface of chalcogenides is essential. Herein, we report a detailed study of a deposition method using thiourea coordinated transition metal complexes. This method allows the preparation of a library of a wide range of single atoms including both noble and non-noble transition metals (Fe, Co, Ni, Cu, Pt, Pd, Ru) with a metal loading as high as 10 wt % on various ultrathin 2D chalcogenides (MoS2, MoSe2, WS2 and WSe2). As demonstrated by the state-of-the-art characterization, the doped single transition metal atoms interact strongly with surface anions and anion vacancies in the exfoliated 2D materials, leading to high metal dispersion in the absence of agglomeration. Taking Fe on MoS2 as a benchmark, it has been found that Fe is atomically dispersed until 10 wt %, and beyond this loading, formation of coplanar Fe clusters is evident. Atomic Fe, with a high electron density at its conduction band, exhibits a superior intrinsic activity and stability in CO2 hydrogenation to CO per Fe compared to corresponding surface Fe clusters and other Fe catalysts reported for reverse water–gas-shift reactions.
In this study, the degradation of a LiFePO4/graphite battery under an over-discharge process and its effect on further cycling stability are investigated.
On‐chip dynamic strain engineering requires efficient micro‐actuators that can generate large in‐plane strains. Inorganic electrochemical actuators are unique in that they are driven by low voltages (≈1 V) and produce considerable strains (≈1%). However, actuation speed and efficiency are limited by mass transport of ions. Minimizing the number of ions required to actuate is thus key to enabling useful “straintronic” devices. Here, it is shown that the electrochemical intercalation of exceptionally few lithium ions into WTe2 causes large anisotropic in‐plane strain: 5% in one in‐plane direction and 0.1% in the other. This efficient stretching of the 2D WTe2 layers contrasts to intercalation‐induced strains in related materials which are predominantly in the out‐of‐plane direction. The unusual actuation of LixWTe2 is linked to the formation of a newly discovered crystallographic phase, referred to as Td', with an exotic atomic arrangement. On‐chip low‐voltage (<0.2 V) control is demonstrated over the transition to the novel phase and its composition. Within the Td'‐Li0.5−δWTe2 phase, a uniaxial in‐plane strain of 1.4% is achieved with a change of δ of only 0.075. This makes the in‐plane chemical expansion coefficient of Td'‐Li0.5−δWTe2 far greater than of any other single‐phase material, enabling fast and efficient planar electrochemical actuation.
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